SQL REPORTING SERVICES 2008 R2

I HAVE THIS QUERY:

SELECT     DIMENSIONS.DESCRIPTION, HOS_SALEHST.CUSTOMERCLASS, MONTH (HOS_SALEHST.INVOICEDATE) as MONTH,
YEAR (HOS_SALEHST.INVOICEDATE) as YEAR, HOS_SALEHST.ITEMCLASS, SUM(HOS_SALEHST.QUANTITY) AS QUANTITY, SUM(HOS_SALEHST.NETSALESAMOUNT)
                      AS NETSALESAMOUNT
FROM         HOS_SALEHST INNER JOIN
                      DIMENSIONS ON HOS_SALEHST.DATAAREAID = DIMENSIONS.DATAAREAID AND HOS_SALEHST.ITEMCLASS = DIMENSIONS.NUM
WHERE     (HOS_SALEHST.INVOICEDATE >= '1/1/2013') AND (HOS_SALEHST.INVOICEDATE < '4/1/2014') AND (HOS_SALEHST.ITEMCLASS <= 1985) AND
                      (HOS_SALEHST.ITEMCLASS <> '') AND (DIMENSIONS.DIMENSIONCODE = 1) AND ((HOS_SALEHST.COMPANYNUM >= 02 AND
HOS_SALEHST.COMPANYNUM <= 07 AND
HOS_SALEHST.CUSTOMERCLASS = 'DS') OR
(HOS_SALEHST.COMPANYNUM = 01 AND
HOS_SALEHST.CUSTOMERCLASS <> 'DC'))

GROUP BY HOS_SALEHST.CUSTOMERCLASS,HOS_SALEHST.ITEMCLASS, DIMENSIONS.DESCRIPTION, MONTH(HOS_SALEHST.INVOICEDATE), YEAR(HOS_SALEHST.INVOICEDATE)
ORDER BY HOS_SALEHST.ITEMCLASS

I want to have it where the SALEHST.CUSTOMERCLASS will pull in the lines t that are 'ES' or 'EC' as EXP but all others pull in as they are.

I tried using the CASE ELSE below but can't get it to work.  Maybe it's not the right approach???

SELECT     DIMENSIONS.DESCRIPTION, HOS_SALEHST.CUSTOMERCLASS, MONTH (HOS_SALEHST.INVOICEDATE) as MONTH,

YEAR (HOS_SALEHST.INVOICEDATE) as YEAR, HOS_SALEHST.ITEMCLASS, SUM(HOS_SALEHST.QUANTITY) AS QUANTITY, SUM(HOS_SALEHST.NETSALESAMOUNT)

                     AS NETSALESAMOUNT

FROM         HOS_SALEHST INNER JOIN

                     DIMENSIONS ON HOS_SALEHST.DATAAREAID = DIMENSIONS.DATAAREAID AND HOS_SALEHST.ITEMCLASS = DIMENSIONS.NUM

WHERE     (HOS_SALEHST.INVOICEDATE >= '1/1/2013') AND (HOS_SALEHST.INVOICEDATE < '4/1/2014') AND (HOS_SALEHST.ITEMCLASS <= 1985) AND

                     (HOS_SALEHST.ITEMCLASS <> '') AND (DIMENSIONS.DIMENSIONCODE = 1) AND ((HOS_SALEHST.COMPANYNUM >= 02 AND

HOS_SALEHST.COMPANYNUM <= 07 AND

HOS_SALEHST.CUSTOMERCLASS = 'DS') OR

(HOS_SALEHST.COMPANYNUM = 01 AND

HOS_SALEHST.CUSTOMERCLASS <> 'DC',

CASE SALEHST.CUSTOMERCLASS

WHEN 'EC' OR 'ES' THEN 'EXP'

               ELSE 'SALEHST.CUSTOMERCLASS'))

GROUP BY HOS_SALEHST.CUSTOMERCLASS,HOS_SALEHST.ITEMCLASS, DIMENSIONS.DESCRIPTION, MONTH(HOS_SALEHST.INVOICEDATE), YEAR(HOS_SALEHST.INVOICEDATE)

ORDER BY HOS_SALEHST.ITEMCLASS

Really appreciate your help.